Squeak Etoys is a "media authoring tool"-- software that you can download to your computer
and then use to create your own media. You can write out your project and share it with others.
Etoys runs on any Mac or Windows machine, as well as on the OLPC XO machine.
It is free.
Find out about Etoys.

Text of this guide (for searching): Paint Tools: Straight Line Tool. Click on the paint palette in your Navigator Bar and then on the white tab on the lower right edge to open or close the straight line tools.
Experiment. Use the straight line tool and hold down shift to make perfect vertical and horizontal lines or forty-five degree angles. Try all six brushes sizes with the straight line tool.